Same distro release, different kernel versions?

I keep them both updated regularly using update manager to ensure a mthtc frontend remote client stays compatible. Both have nvidia video adapters. The htpc has AMD and 4GB memory and the wrksta64 has Intel Quad with 8GB memory.

Now they have different kernel versions.

keepitsimpleengr@wrksta64:~$ uname -r
2.6.35-28-generic

keepitsimpleengr@htpc64:~$ uname -r
2.6.35-30-generic

linux-headers-2.6.35-30 and linux-headers-2.6.35-30-generic are installed on wrksta64 but not linux-image-2.6.35-30-generic
All three are installed on htpc64

The general answer, which you already know, is that this happened because linux-image-generic was not installed. If you have now installed linux-image-generic, then this should not happen again. If you have only installed the specific package for the new kernel, whose name is similar to that but has a version number as part of the time, then this *will* happen again.

As for why it was that linux-image-generic was not installed, I don't know. If you want to investigate it, you could examine the logs (/var/log/dpkg.log and the rotated logs /var/log/dpkg.log.1, /var/log/dpkg.log.2.gz and so forth), and search for it.